In order to reduce power consumption and increase performance, circuits having devices with different threshold voltages have been used in different portions of the integrated circuit. Devices with low threshold voltages are faster, but have greater sub-threshold voltage leakage (consume more power) compared with devices having high threshold voltages but low sub-threshold voltage leakage. Using a mix of high threshold voltage devices on non-performance critical circuit paths and low threshold voltage devices on performance critical circuit paths can result in lower overall power consumption and higher performance than using devices having the same threshold voltages.
However, it is critical that the designed relationship between the different threshold voltage values of different-threshold voltage devices be maintained in the fabricated integrated circuit in order to ease timing closure during design and avoid signal propagation timing issues. Therefore, there is a need for methods and circuits for maintaining the design values and/or relationships between the different threshold voltage values of multiple threshold voltage devices.